Reduction of interference



March 10, 1931. J. HERMAN 1,795,393

REDUCTION OF INTERFERENQE Original Filed March 15, 1930 Oscz'llatons .Semdzhyflltens ll'unsmt er Radio .Bec.

INVENTOR L Jfiel/w/ew/z/ ATTORNEY Patented Mar. 10, 1 931 UNITED .sT T s PATENT OFFlCE aossrn HERMAN, or wEsrrmLn, new JERSEY, assrenoa ro AMERICAN, TELEPHONE 4ND rrmnoaarn COMPANY, A coaroaa'rron or NEW Yomr imnuc'rron or i'nrnarannncn Application filed larch 15, 19 80, 8eria1 1\o. 438,230.' [ne newed' oetober 11, 19 80.

This invention relates to telegraph trans mission systems and more particularly to I means for reducing interferenceinsuch sys tems. H

In accordance with the presentinvention.

- telegraph signals are transmitted by apply ing currents of two-different frequencies inted corresponds to amarking ,si

c'eiving the marking frequency and the other for receiving the spacing frequency. The currents in the two paths are'thencaused to actuate separate windings ofa" polar receiving relay so that the relay armatureoperates, against one contact when one of the currents is received and against the other contact when the other current is received. ';The current flowing in either path is also utilized to disable the other path, with theresult that when current of one frequency is being'received, an

interfering currenthaving a frequency 'SliCh that it may be received in. the other path will not cause false operation. The system also has the advantage that fairly large variations in transmission equivalents will have practically no effect upon the bias of the received signals since the effect upon the marking and spacing currentswill be substantially the same.

The invention will now be more fully understood from the following description when read in connection with the accompanying drawing in which Figure 1 is-a circuit diagram showing theapparatiis at a sending station; Fig. 2 is a circuit diagram showing the apparatus at a receiving station; and Fig.

3 is a circuit" diagram showing a modified form of the receiving apparatus.

Referring to Fig.1, the operation of the v s e n'ding key K controls the sending relay SR whose contact in turn determines the transmission of a frequency from either of two oscillators 0 or 0 When the armature of the sending relay SR rests upon its spacing contact 8, the output of the oscillator 0 is short-circuited and current of frequency f, is

transmitted from the oscillator 0 through received this frequency, will the resistanc'e wand thence through the sending filterSF to the radio transmitter RT. The currentv thus transmitted corresponds to a spacing signal. When the armature of the relay SR rests upon its marking contact m, th'e output ofthe oscillator 0 is short-circuited and thefrequencyj is transmitted through the resistance '0 and through the sending filter SF to the radio transmitter RT; .The'current so transmitted corresponds ,toa marking signal. .With this arrangement, when the key K is operated to send telegraph signals,,current of one of the two frequencies quencies sent out under the control of the key K at the transmitter. Two receiving paths are provided, one for receiving the marking frequency, and the other for receiving the spacing frequency. When the marking frequency f,,, is received it'passes through a receiving filter-RF to an amplifier A, the

output of which is coupled through a transformerT to a rectifying arrangement R The rectifying'arrangement R consists of four rectifying elements of any known type connected in a bridge circuit, as shown, .so that when alternating current flows in the secondary of -the transformer T the half waves of eitherdirection which are applied to two of the terminals of the bridge produce a one-way potential always in the same direc: tion across the other two terminals of the bridge. The result is that a rectified current will flow through the resistance 7' and through the winding W, of the polar receiving relay, thereby causing the armature to be held against the marking contact m. Similarly, if a spacing frequency f is being selected through the receiving filter RF and applied to the amplifier A The output of the amplifier is coupled through a. transformer T to a rectifying arrangement R similar to that already described. Consequently, when the received alternating current flows in the output circuit of the amplifier A a one-way quencies f and i will be received at all times and only-one of said frequencies will be received at any given instant. Consequently, if the marking frequency is being received the receiving polar relay will have its armavaried, however, if static or other disturbing ture 'shifted to its marking contact and the receiving apparatus in the spacing path will have no eflect to shift the armature in the opposite direction. Likewise, if the spacing frequency is received, the receiving apparatus in the marking path will be without effect upon the receiving armature which will be moved and held against thespalcing contact. If under these conditions the transmission equivalent of vthe circuit should change, both the marking and spacing frequencies would be subjected to substantially the same change in transmission with the result that the bias of the receiver as between marking and spacing would not be materially altered.

The conditions just described might be currents were received. Suppose, for ex-.

ample, that the marking frequency f is being received and at the same time a static discharge should occur which would result in a frequency corresponding to i being applied to the filter RF This would result in a flow of current through the winding W of the r ceiving relay at the same time that the desired signal is actuating the winding W This might result in causing a false spacing signal by shifting the armature to the spacing con tact. Similarly, during the receipt of a spacing frequency f, a static discharge might cause a component corresponding to f to enter the receiving filter RF This would result in an unwanted current flowing through the winding W of the polar,receiving relay at the same time that the desired spacing current flows through the winding order to prevent such false action, a.

connection extends from the upper and lower terminals of the rectifying arrangement R tothe grid circuit-of the amplifier A of the opposite path so that when a rectified potentie! is produced across said terminals said rectified potential will be in such a direction as to cause the grid of the amplifier A to be 'so negative that no current can flow in its output circuit even when an alternating current component corresponding to static is superimposed upon the grid. In other words, the rectified current from-the rectifying ar rangement It is utilized to paralyze the amplifier A andthereby to render the spacing path inoperative durin' the presence of the wanted marking signa The receivin relay, therefore, cannot shift its armature rom marking to spacing untilthe marking frequency ceases.- Similarly, a connection is -made between the upper and lower terminals ture from spacing to marking until the wanted spacing current ceases.

By means of the arrangement above described, while either the marking or spacing path. is receiving its desired frequency, the other path is disabled so that an interfering frequency corresponding to the other path will be without effect until the path having control of the receiving relay no longer receives its frequency. In passing it may be 'noted that the rectified potentials supplied by the rectifier arran ements R and R may be smoothed out bytl ie provision of condensers C and C bridged across the output terminals of the rectifiers, or by means of inductances connected in series in the output clrcult, or by means of a comblnatlonof .inductances and condensers.

A modified receiving arrangement is shown in Fig. 3. Here the output circuits of the amplifiers A and A of the marking and spacing paths, respectively, are connected to detectors D and D whose output circuits supply detected currents to operate the marking and spacing windings W and W respectively, of the polar receiving relay. In order that when either the marking or spacing frequency is being received the other channel may be disabled to prevent false operation due to interference, the alternating current component appearing in the output "circuit of each detector, which is normally by-passed through condensers such as G and C respectively, is caused to flow through the primary windings of the transformer T in the case of the marking path, and the transformer T in the case of the spacing path.

Rectifying arrangements R and R are associated with the secondaries of these transformers in the manner described in connection with Fig. 1, and the rectified potential from these rectifiers is applied to the grid circuits of the amplifiers of the opposite aths. The result is that when the marking requency is being received, for example, the rectifier R will rectify a frequency corresponding to the marking signal appearing in' the output circuit of the, detector D and paralyze the amplifier A to prevent an interout the rectified ,potentials, and resistances r' and 1 are provided for discharging the capacities.

The circuits above described are illus trated in connectionwith radio transmission from the sending station to the receiving station and for this reason a radiotransmitter RT and a radio receiver RR have been symbolically indicated. It will beunderstood, however, that the invention-is not limited to radio transmission but maybe employedfor carrier transmission over wire lines by connecting the transmitting station and the receivingstation by any known type of carrier transmission circuit.

1 It will beobvious that the general prin-- ciples herein disclosed may be embodied in many other organizations widely different from those illustrated without departing from the spirit of the invention as defined in the following claims.

What is claimed is:

1. In a transmission system having means for transmitting one frequency for marking and another frequency for spacing signals, a

receiver comprising two paths, means for selecting the marking frequency into one path,

means for selecting the spacing frequency into the other path, and means controlled by a current flowing in either path for disabling the other path. p

2. ,In a transmission system having means for transmitting one frequency for marking and another. frequency or spacing signals, a receiver comprising two paths, means for selecting the marking frequency into one path, means for selecting the spacing frequency into the other path, means controlled by a current flowing in either path for disabling the other path, and a receiving relay having separate windings controlled by the currents flowing in the two paths.

3. In a transmission system having means for transmitting one frequency for marking and another frequency for spacing signals, a receiver comprising two paths, means for selecting the marking frequency into one path, means for selecting the s acing frequency into the other path, a recti er arrangement associated with each path for producing rectified potentials in response to the currents flowing in the respective paths, and means whereby the rectified potentials produced by either rectifying arrangement will cause disablement of the opposite path.

4. In atransmission system having means I for transmitting one frequency for marking and another frequency for spacing signals, a receiver comprising two paths, means for selecting the marking frequency into one path, means for selecting the spacing frequency into the other path, a rectifier rangement associatedwith each path for producing rectified potentials in response to the currents flowing in the respective paths,

means whereby the rectified potentials produced by either rectifying arrangement will 'cause disablement of the opposite path, and

areceiving relay having separate windings conltlrolled by currents flowing in the two pat s.

5. In a transmission system having means for transmitting one frequency for marking and another frequency for spacing signals, areceiver comprising two paths, means for selecting the marking frequency into one path, means for selecting the spacing frequency into the other path, an amplifier in each path, and means controlled by currents received in either path for disabling the amplifier in-the opposite path.

6. In a transmission system having mean for transmitting one frequency for marking and another frequency for spacing signals, a receiver comprising two paths, means for selecting the marking frequency into one path, means for selecting the spacing frequency into the other path, an amplifier in each path,,means controlled by currents received in either path for disabling the amplifier in the opposite path, and a receiving relay having separate windings. controlled by currents flowing in the two paths.

7. In'a transmission system having means for transmitting one frequency for marking and another frequency for'spacing signals, a receiver comprising two paths, means for selecting the marking frequency into one path, means for selecting the spacing frequency into the other path, an amplifier in each path, a rectifying arrangement associated with each path for producing rectified potentials in response to currents flowing in the paths, and means whereby rectified potential supplied by each rectifying arrangement disables the amplifier of the opposite path.

8. In a transmission system having means for transmitting 'one frequency for marking and another frequency for spacing signals, a receiver comprising'two paths, means'for selecting the marking frequency into one path, means for selecting the spacing frequency into the other path, an amplifier in each path, a rectifying arrangement asso- 'ciated with each path for producing rectified potentials in response to currents flowlng in the paths, means whereby rectified potential supplied by each rectifying arrangement disables the amplifier of the opposite path, and a receiving relay having separate windings controlled by the currents flowing in the two paths. a

- 9. In a transmission system having means for transmititng one frequency for marking and another frequency for spacing signals, a receiver comprising two paths, means fa selecting the marking frequency into onepath, means for selecting the spacing frequency-into the other path, an amplifier in each path, a rectifying arrangement assoc1- ated with each path comprising four rectifiers connected in a bridge having two of its terminals so associated with the path that in response to alternating currentsflfiowing in the path a rectified potential will be produced at the opposite terminals of the bridge,

and means controlled by, the rectified potential supplied by each'rectifying arrangement for disabling the amplifier of the opposite ath. v P 10. In a transmission system having means for transmitting one frequency for marking and another frequency for spacing signals, a receiver comprising two paths,-means for se lecting the marking frequency into one path, means for selecting the spacing frequency into the other path, an amplifier in each path, a rectifying arrangement associated with each path comprising four rectifiers connected in a bridge having two of its terminals so associated with the path that in response to alternating currents flowing in the path a rectified potential will be produced at-the opposite terminalsof the bridge, means controlled by the rectified potential supplied by each rectifying arrangement for disabling theamplifier of the opposite path, and a receiving relay having separate windings controlled by the currents flowing in the two paths.

. 11. In a transmission system havingmeans for transmitting one frequency for one signaling condition and another frequency for another signaling condition, a receiver comprising two paths, means for selecting the o'negv frequency into one path, means for'selectin'g the other frequency into the other path,a= rectifier arrangement associated with each' path for producing rectified potentials in res onse to the currents flowing in the respective paths, and means whereby the rectified potential produced by either rectifying arrangement will cause disablement of the opposite ath.

' 12. n a transmission system having means I for transmitting one frequency for one signaling condition and another frequency for name to this specification this 14t another signaling condition, a receiver comprising two paths, means for selecting the one ing the other frequency into the other path,

an amplifier in each path, a rectifying arrangement associated with each path for producing rectified potentials in response to currents flowing in the paths, and means whereby rectified potentials supplied by each rectifying arrangement disables the amplifier of the opposite path.

14. In a transmission system having means for. transmitting one frequency for one signaling condition and another frequency for another signaling condition, a receiver comprising two paths, means for selecting the one frequency into one path, means for selecting the other frequency into the other path,'an

amplifier in each path, a rectifying arrangement associated with each path comprising four rectifiers connected in a bridge having two of its terminals so associated with the.

path that in response to alternating currents flowing inthe path avrectified potential will be produced at the opposite terminals of the bridge, and means controlled by the rectified -potential supplied by each rectifying arrangement for disabling the amplifier of the opposite path. n 1

"In testimony whereof, have si ned my Ii day of March, 1930.

JosriPH HERMAN. 

